Pitch is advantageous for producing carbon fibers or other high strength, high density molded carbon materials.
Optically anisotropic pitch compositions suitable for producing high performance carbon fibers are described in the specification of the previously filed Japanese Patent Application No. 162972/1980. As the result, it has now been found that an optically anisotropic pitch is a pitch having good molecular orientation with a developed laminate structure of fused polycyclic aromatics, but, in fact, it contains various kinds in mixture, among which, those having low softening points and suitable for the production of homogenous carbon fibers have specific chemical structures and compositions, that is, in the optically anisotropic pitch, the composition, structure and molecular weight of Component O, i.e. a component soluble in n-heptane and Component A, i.e. a component insoluble in n-heptane and soluble in benzene are extremely important. More specifically, it has been found that a pitch composition containing specific amounts of Component O and Component A can be present as an optically anisotropic pitch and that appropriate adjustment of the composition balance is an essential requirement on an optically anisotropic pitch composition for practically producing a high performance carbon fiber.
Further, it has also been found that by specifying the remaining components in the pitch composition other than the aforesaid Component O and Component A, that is, a component insoluble in benzene and soluble in quinoline (hereinafter referred to as Component B) and a composition insoluble in quinoline (hereinafter referred to as Component C), an optically anisotropic pitch for producing an even further excellent high performance carbon material may be provided.
Still further, as the result of the more detailed study in the respective characteristics of the aforesaid respective components and on the relationships between the contents of the respective components having said characteristics and the properties, homogeneity, orientation etc. of the total pitch, the present inventors have discovered it important that the respective components have specific properties. In other words, it has been discovered that for the properties of the constituting components of an optically anisotropic pitch having high orientation, homogeneity and a low softening point required for producing a high performance carbon fiber and capable of being melt spun stably at low temperatures, the C/H atomic ratio, the ratio of the carbon atoms in the aromatic structure to the total carbon atoms fa (hereinafter referred to as the fa or the aromatic carbon fraction), the number average molecular weight, the maximum molecular weight (the molecular weight at a point where 99% has been integrated from the lower molecular weight side) and the minimum molecular weight (the molecular weight at a point where 99% has been integrated from the higher molecular weight side) are specified within the ranges hereinbelow described.